The present inventive concept herein relates to temperature sensing fields, and more particularly, to a process independent temperature sensor based on an oscillator.
A temperature sensor using a semiconductor device is classified into two types.
One type is a voltage-domain temperature sensor sensing a BJT (bipolar junction transistor) output current obtained through a BJT as an analog voltage proportional to a temperature, and then converting the analog voltage into a digital signal to output it.
The other type is a time-domain temperature sensor detecting a signal delay which changes depending on a temperature change and outputting the delay signal as a digital signal through a digital converter.
A recent temperature sensor has a high sensing accuracy by applying technologies of a dynamic element matching (DEM), an offset cancelation and a curvature correction. However, since applying the technologies complicates a chip of temperature sensor, complexity of chip makes it difficult to apply the chip of temperature sensor to a system on-chip (SoC). Complexity of chip makes it difficult to apply the chip of temperature sensor to a simple use and a mobile use.
FIG. 1 is a view illustrating a comparison of operation concept of conventional voltage-domain temperature sensor and conventional time-domain temperature sensor.
As illustrated in an upper portion of FIG. 1, the voltage-domain temperature sensor has a structure obtaining a temperature sensing output through a comparator C1. In a voltage-domain temperature sensor based on a BJT, an output of temperature sensor is different depending on a process deviation. Thus, an output of temperature sensor is different between chips of temperature sensor. Also, there is a problem that an analog circuit is complicated and power consumption is high.
As illustrated in a lower portion of FIG. 1, a time-domain temperature sensor has a structure obtaining a temperature sensing output through a flip-flop D1. In the time-domain temperature sensor, the chip is relatively less complicated and a low power characteristic is relatively good. Since the time-domain temperature sensor adopts relatively a lot of digital circuits, it has an advantage when integrating a chip. Therefore, a study of the time-domain temperature sensor is more actively underway as compared with the voltage-domain temperature sensor.
However, since the time-domain temperature sensor and the voltage-domain temperature sensor need a post calibration for two temperature points, production costs increase.
The time-domain temperature sensor needs a temperature output compensation circuit for improving an accuracy of temperature output. Since an adoption of the temperature output compensation circuit requires a high cost, it is not easy to adopt the temperature output compensation circuit. Moreover, since the time-domain temperature sensor needs an external reference clock signal, circuit complexity of temperature sensor module may increase.